DESCRIPTION: (provided by the applicant): This is a revised, new application to examine the role of dendritic cells (DC) in the induction of Th2 responses to schistosome antigens. Initiation of the immune response to extracellular pathogens such as schistosomes occurs when DC present antigen (Ag) peptides to CD4+ T helper (Th) cells. This signal, along essential co-stimulatory signals from other DC surface molecules, promotes clonal expansion of T cells expressing relevant TCR. Thereafter the immune response focuses such that the majority of Th cells proceed to produce similar panels of effector cytokines. The outcome is usually an immune response dominated by Th1 or Th2 cells, where Th1 cells make IFN-g and IL-2, whereas Th2 cells make IL-4, -5, -6, -10 and -13. Expression of the transcription factors T-bet or GATA3 are respectively essential for acquisition of the Th1 or Th2 phenotype. IL-12 selects strongly for Th1 cells and IL-4 selects for Th2 cells. DC participates in Th1 by making IL-12 directly in response to certain microbial pathogens and upon ligation of CD40 by CD 154. However, little is known of the DC response to pathogens that induce Th2 responses. The hypothesis to be tested is that DC, by recognizing pathogen associated molecular patterns on schistosome Ag, respond in a way that is yet to be fully characterized, but which is distinct from their response to Th1 Ag, to orchestrate the development of a Th2 response. The following specific aims are designed to test this hypothesis: Specific Aim 1) To delineate the differences in the response of DC to schistosome Ag (which induce Th2 responses) versus their response to Th1 Ag (e.g., Propionebacterium acnes). Specific Aim 2) To link DC phenotype following exposure to schistosome Ag to the induction of Th2 responses by these Ag, with a focus on the role of soluble mediators and on co-stimulatory signals. Specific Aim 3) To assess the function of DC in promoting Th1 and Th2 responses in vivo following the injection of Ag and during infection. We will use micro-arrays, proteomics and subtractive cDNA libraries to identify genes expressed specifically by schistosome Ag-stimulated DC, combined with an adoptive transfer system in which DC are pulsed with Ag in vitro and injected into mice to examine the influence of identified genes on Th response outcome. DC activation during infection will be examined and the interaction of DC with other immune system cells will be investigated using flow cytometry and immunofluorescence microscopy. The long-term goal of this approach is to more fully understand the function of DC in polarized T cell response initiation with a view to improving vaccination or immuno-therapy strategies. .